1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel with a direct backlight.
2. Description of the Prior Art
A liquid crystal display (LCD) panel has been utilized in a wide field of such as audio-visual (AV) machines, office automation (OA) machines, and portable terminal devices because of its features that it is fabricated to be thin, light in weight and low in power consumption. A backlight for the LCD panel is classified into a direct type, an edge light type, a surface light source type, and an external light type depending on its illumination style.
As shown in FIG. 1, for example, a conventional LCD panel 300 with a direct backlight comprises a lamp unit 6 for holding a plurality of lamps serving as a backlight source, an optical sheet 5 for converting backlight to uniform illumination light, and a liquid crystal panel 3 sandwiching liquid crystal between a pair of substrates opposed to each other as main constituent components.
Furthermore, the conventional LCD panel 300 with the direct backlight comprises a housing for fixedly holding these components thereto (including a front side shield 2, a rear side shield 7 serving also as a reflector for reflecting the backlight, and an internal chassis 4 for positioning the liquid crystal panel 3 in the constitution of FIG. 1); and a board (a circuit board 8 for driving the liquid crystal panel 3 and an inverter board 9 for driving a lamp) held and fixed to the housing (the rear side shield 7 in FIG. 1) as constituent components.
Herein, when the LCD 300 is used as a monitor of a personal computer, a panel size needs not to be made so large. Therefore, even in the foregoing constitution, rigidity of the LCD panel 300 can be maintained, and sufficient brightness can be obtained. However, when the LCD panel 300 is used as a television set, the panel size needs to be made large, for example, about 20-inch class panel. For this reason, a slight external force for the LCD panel 300 strains the LCD panel 300, and this strain causes display unevenness.
Furthermore, since the brightness needs to be increased when the LCD panel is used for the television set, the number of lamps of the backlight must be inevitably increased.
Therefore, when the number of the lamps is increased, temperature of the constituent components such as the liquid crystal panel 3, the circuit board 8, and the inverter board 9 rises due to heat generation of the backlight of the LCD panel 300, and thus its performance is degraded.
Accordingly, in order to increase the rigidity of the LCD panel 300, it is conceived to realize a strong structure of a housing such as a frame and a chassis for fixedly holding the liquid crystal panel 3, the lamp unit 6 and the like. However, in this case, the housing itself becomes large-sized, and it is impossible to achieve a narrower picture frame size of the LCD panel 300. Moreover, weight of the LCD panel 300 increases.
Furthermore, as a measure to hold down the temperature rise of the constituent components due to the heat generation of the backlight, there is a measure in which heat radiation means is provided in a structural body (for example, the rear side shield 7 in FIG. 1) for fixedly holding the lamps of the backlight or the like. This measure is disclosed in, for example, Japanese Patent Laid-Open No. Sho 63(1988)-5321.
Specifically, a LCD panel, which increases radiation efficiency by providing radiation fins on a reflector for reflecting light emitted from a fluorescent tube, is disclosed. In addition, in Japanese Patent Laid-Open No. Sho 63(1988)-20128, a LCD panel having a structure in which a supporting component is provided in both ends of a radiation plate and thereby a light source is fitted thereto, is disclosed. This LCD panel disclosed herein increases the radiation efficiency by providing radiation fins on a rear surface side of the radiation plate.
However, in the structures described in the foregoing official gazettes, a host of fins are provided in the structural body for fixedly holding the lamps of the backlight and in the radiation plate. Accordingly, it is natural that heat generated by the backlight can be discharged with using the radiation fins. However, the provision of the fins in the structural body and the radiation plate increases the cost. This is a serious problem for the LCD panel for which a lower price is required.
On the ground that the structural body and the radiation plate becomes heavier and larger due to the provision of the host of fins, a weight reduction and a reduction in thickness of the LCD panel are hindered. This problem becomes evident more significantly as a panel size becomes larger.
Furthermore, when the panel size becomes larger, there is a problem that air heated by the heat of the backlight remains above a panel surface, in addition to the problem of the temperature rise due to the above described heat generated by the backlight. A problem that the remaining of the air elevates temperature of peripheral components and a temperature gradient occurs in the panel surface is also raised.
For example, in a 20-inch class LCD panel in which power consumption of the backlight is about 50 W, a temperature at an upper portion of the panel becomes higher than that at a lower portion of the panel by about 10° C. Thus, when the panel size is large, not only heat radiation but also an evenness of a temperature distribution are required. However, since no consideration for the temperature gradient in the panel surface is taken in the above described official gazette, characteristics of thin film transistors, optical properties of liquid crystal, and the like change owing to the temperature gradient. Thereby, display unevenness occurs, leading to significant deterioration of display quality.
The present invention has been made invented in view of the foregoing problems, and a principal object of the present invention is to maintain the rigidity of a LCD panel even when a panel size becomes larger. Additionally, an object of the present invention is to provide a LCD panel comprising a direct backlight, which can achieve an increase in brightness, by suppressing rise in temperature of constituent components of a liquid crystal panel and a substrate due to heat generation of a backlight source as well as a temperature gradient in a panel surface.